1. Field of the Invention
The present invention relates to a semiconductor device.
2. Description of Related Art
In recent years, a semiconductor device having a plurality of semiconductor chips (e.g., an MCP (Multi Chip Package) and a POP (Package On Package) are known. In such a semiconductor device, two or more semiconductor chips are disposed adjacent to each other. In a case where such a semiconductor device has two semiconductor chips, one of which is a flash memory chip (first memory chip) and the other is a DRAM (Dynamic Random Access Memory) chip (second semiconductor chip), a temperature of the DRAM rises along with a temperature rise of the accessed flash memory chip. The DRAM chip may malfunction due to the temperature rise. In order to prevent such malfunction of the DRAM chip, such a semiconductor device changes a period of refresh operation for data retention of a memory cell in the DRAM chip (second semiconductor chip) in response to an access request made to the flash memory chip (first semiconductor chip) (refer to Japanese Patent Application Laid-Open No. 2009-163585).
However, in the above-described semiconductor device having the flash memory chip and DRAM chip, in order to prevent the malfunction of the DRAM chip, a period of the refresh operation (refresh period) in the DRAM chip is inevitably changed in response to an access request made to the flash memory chip. Therefore, even when the temperature of the flash memory chip does not rise actually, the refresh period of the DRAM chip may often be shortened. Thus, in the semiconductor device as described above, the refresh period of the DRAM chip (second semiconductor chip) is changed for each access request to the flash memory chip (first semiconductor chip) regardless of whether necessary or not, increasing the number of times of the refresh operation, which unnecessarily increases current consumption.
As described above, the above-described semiconductor device has a problem in that the refresh period is unnecessarily changed to result in wasted current consumption.